Chemical analysis of liquids, such as water, milk and biological fluids is often desirable or necessary for health maintenance and diagnostic treatment. Various compositions and elements to facilitate such analyses are known. Such compositions and elements generally include a reagent composition for determining a substance under analysis, termed an analyte herein. The analyte can be a biological organism or a chemical substance. This reagent composition, upon interaction with the analyte, provides a detectable change (e.g. dye formation).
Recently, much work has been directed to developing compositions and elements which are useful for rapid and highly quantitative diagnostic or clinical analysis of biological fluids such as whole blood, serum, plasma, urine and the like.
For the rapid and effective diagnosis and treatment of infectious diseases, it is desirable to be able to detect the bacteria causing the disease as rapidly as possible. Infections of the urinary tract are among the most common bacterial diseases, second in frequency only to infections of the respiratory tract. In fact, in many hospitals, urinary tract infections are the most common form of nosocomial infections, often following the use of catheters and various surgical procedures. Most urinary tract infections (UTI) result from ascending infection by microorganisms introduced through the urethra and vary in severity from an unsuspected infection to a condition of severe systemic disease. Such infections are usually associated with bacterial counts of 100,000 (10.sup.5) or more organisms per mL of urine, a condition referred to as significant bacteriuria. Under normal conditions, urein is sterile, although contamination from the external genitalia may contribute up to 1,000 (10.sup.3) organisms per mL in properly collected and transported specimens.
Significant bacteriuria may be present in a number of pathological conditions involving microbial invastion of any of the tissues of the urinary tract, or may result from simple bacterial multiplication in the urine without tissue invasion. The infection may involve a single stie such as the urethra, prostate, bladder, or kidney, although frequently it involves more than one site. Infection restricted to the urine may present itself as asymptomatic bacteriuria, i.e., a condition which manifests no overt signs or symptoms of infection. Early treatment of this condition can prevent the development of more serious conditions, e.g., pyelonephritis (inflammation of the kidney and the renal pelvis). The rapid detection of bacteria by a reliable method would therefore facilitate an early and specific diagnosis.
Further, in order to insure that a prescribed antiobiotic is in fact effective in treating an infection, repeated tests during therapy are required. The need for simple, rapid bacteriuria tests is thus clear. Moreover, in view of the frequent unsuspected asymptomatic occurrences of UTI among children, pregnant women, diabetics and geriatric populations, diagnosis of which may require collection and testing of several specimens, bacteriuria tests must be sufficiently simple and economical to permit routine performance. Again, this illustrates the need for a rapid and inexpensive bacteriuria detection method.
Determination of certain analytes, notably living cells (such as bacteria, yeast, etc.), is best accomplished using a reduible composition which provides a detectable species in the presence of an electron transfer agent (ETA). The electron transfer agent is first reduced by the living cell. The reduced ETA then reduces the reducible composition to generate a detectable species which is then detected. Phenazine methosulfate (PMS) is a typical ETA.
Unfortunately, PMS and structurally related ETAs are unstable in aqueous solutions. In the related application mentioned above relating to ETAs (U.S. Ser. No. 699,374), there is disclosed an improved class of ETA compounds. These compounds are substituted benzoquinones or naphthoquinones. The ETAs of that invention provide many advantages over the previously known ETAs. However, still further improvements were sought. More particularly, the specific ETAs in the examples of that application have less than the desired sensitivity. Improved sensitivity was particularly sought with the reagents described in the copending applications described above.